1. Field of the Invention
The present invention relates to a brazing structure including a ceramic member and a tubular metal fitting brazed thereto, a ceramic heater, and a glow plug. In more particular, the present invention relates to a brazing structure, such as a ceramic heater, used for a soldering iron, a hair iron, an oil-stove igniter, an oil-stove vaporizer, a sealing device, an automobile oxygen sensor, or a glow plug.
2. Description of the Related Art
Heretofore, brazing structures each including a ceramic member and a metal fitting brazed thereto have been used in various industrial devices and instruments and have also been widely used in various application fields. Among the brazing structures described above, a ceramic heater has been widely used, for example, as a semiconductor heating element, an oil vaporization heat source for an oil fan heater or the like, and a heat source for an automobile oxygen sensor, a glow system, or the like. In particular, in recent years, the demand for automobile ceramic heaters has been increasing.
Ceramic heaters having various shapes, such as a plate, a cylindrical, and a tubular shape, have been generally used. FIG. 1 is a cross-sectional view showing the structure of a glow plug having a tubular ceramic heater. In a related ceramic heater 40 as shown in FIG. 1, in one end side of a ceramic member 41 made of insulating ceramics, a coil made of a high melting point metal (such as tungsten) or a heat resistor 42 made of electrical conductive ceramics or the like is buried. An extension portion 43a of this heat resistor 42 at a cathode side is extended through a side surface of the ceramic member 41 and is connected to a tubular metal fitting 44. In addition, an extension portion 43b at an anode side is connected to one end of an electrode lead metal fitting, which is located at an end side opposite to the end side of the ceramic member 41 in which the heat resistor 42 is buried. Furthermore, an external connection terminal 45 is connected to the other end of the electrode lead metal fitting (see Japanese Unexamined Patent Application Publication No. 2002-122326).
However, in the field using the automobile ceramic heaters, the demand of which has been increasing as described above, in order to improve fuel consumption and/or to clean exhaust gas of a diesel engine, an attempt has been made to increase a pressure in combustion by an increase in compression ratio in the engine. Accordingly, even under severe circumstances, such as a high temperature and/or a high pressure, a brazing structure having a highly reliable brazed-welded portion between a ceramic member and a tubular metal fitting has been required.
Accordingly, the present invention has been conceived in consideration of the circumstances described above, and an object of the present invention is to provide a highly reliable brazing structure including a brazed-welded portion which has superior durability even under severe circumstances, such as a high temperature and/or a high pressure.